UNC-CHAPEL HILL (US) — Ultrasound equipment commonly used for physical therapy reduces sperm counts in lab rats to levels that would result in infertility in humans.

Ultrasound’s potential as a male contraceptive was first reported nearly 40 years ago. However, the equipment used at that time is outdated and no longer available.

As reported in the journal Reproductive Biology and Endocrinology, researchers used those experiments as a starting point to see if modern ultrasound equipment could be used as an effective male contraceptive.

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The team found that by rotating high frequency (3MHz) ultrasound around the testes they were able to cause uniform depletion of germ cells through the testes.

“Unlike humans, rats remain fertile even with extremely low sperm counts. However, our non-invasive ultrasound treatment reduced sperm reserves in rats far below levels normally seen in fertile men,” says James Tsuruta, assistant professor in the Laboratories of Reproductive Biology at the University of North Carolina at Chapel Hill. “However, further studies are required to determine how long the contraceptive effect lasts and if it is safe to use multiple times.”

The best results were seen using two sessions consisting of 15 minutes ultrasound, two days apart. Saline was used to provide conduction between the ultrasound transducer and skin, and the testes were warmed to 37 degrees centigrade. Together this reduced sperm to a Sperm Count Index of zero (3 million motile sperm per cauda epididymis).

The World Health Organization has defined oligospermia (low sperm concentration) as less than 15 million sperm per milliliter. Ninety-five percent of fertile men have more than 39 million sperm in their ejaculate.